Mapping Cortical Development Using Diffusion Tensor Imaging - PowerPoint PPT Presentation

Jeff Neil, MD, PhD

Departments of Neurology, Radiology and Pediatrics

MR Imaging

• Detect signal from 1H of H2O, which is present at a concentration of approximately 100 M.
• In conventional imaging, signal intensity (greyscale) is related to MR relaxation properties of 1H2O such as T1 or T2 relaxation times.
• Water in grey matter has different T1 and T2 relaxation times than water in white matter or CSF.

Water motion in white matter

Parallel to axons

Perpendicular to axons

Hindered Diffusion

(diffusion ellipsoid)

without hindrance

with hindrance

WILSON

Ellipsoid Image

Pierpaoli and Basser, Toward a Quantitative Assessment of Diffusion Anisotropy, Magn. Reson. Med, 36, 893-906 (1996)

Information available through DTI -- Dav

• Related to the overall size of the ellipsoid.
• Values for Dav change with brain maturation.
• Values of Dav change dynamically after injury (useful for early detection of injury).

Diffusion MR Imaging of Stoke

Five hours after onset right hemiparesis and aphasia

DWI

T2W

Courtesy of Jonathan Lewin, Case Western Reserve/UH of Cleveland

Information available through DTI -- Aσ

s

av

• Related to the shape of the ellipsoid
• Independent of Dav (normalized)
• Zero for a sphere, positive for other shapes
• Sensitive to myelination and cortical development

Normal Adult Brain

(A maps)

Information available through DTI – Orientation of λ1

• Useful for following white matter tracts

Conturo et al. Tracking neuronal fiber pathways in the living human brain PNAS96, 10422-10427 (1999).

I. Diffusion Anisotropy in Cortical Grey Matter – Human Studies

McKinstry et al. Radial organization of developing human cerebral cortex revealed by non-invasive water diffusion anisotropy MRI, Cereb Cortex, 12, 1237-1243 (2002).

Background

• Nonzero values for diffusion anisotropy have been described occurring transiently during the cerebral cortical development:
• Cat [Baratti et al. Proc ISMRM, 5th Annual Meeting and Exhibition, Vancouver 504 (1997)]
• Pig [Thornton et al. Magn Reson Imaging15, 433-440 (1997)].
• We measured cerebral cortical anisotropy values from premature newborn infants.

Whisker Plot: 26 Weeks GA

Whisker Plot: 35 Weeks GA

Diffusion Anisotropy: Cerebral Cortex

M. Marin-Padilla J Comp Neurol321, 223 (1992)

Cortical Anisotropy Conclusions

• Cerebral cortex in infants less than 36 weeks gestational age (GA) has nonzero anisotropy values.
• Cortical A values decrease with increasing GA (rank sum = -0.94, p < 0.01) and are consistent with zero after 36 weeks GA.
• Changes in diffusion anisotropy reflect changes in underlying cortical architecture.
• Diffusion anisotropy measures may have a role in assessing cortical development and its response to injury.

II. Diffusion Anisotropy in Cortical Grey Matter – Preliminary Baboon Data

Experimental Design

• Evaluated immersion-fixed tissue supplied by the Southwest Foundation in San Antonio (Drs. Jackie Coalson, Brad Yoder, Don McCurnin).
• Specimens available from 90 days (20 weeks) through 182 days (40 weeks).
• 450 mm3 spatial resolution.
• 40 q or b values
• Bayesian probability theory for model selection and parameter estimation (Drs. Chris Kroenke, G. Larry Bretthorst).

No Constant

Diffusion + C

Model

Selection

No Signal

Constant

Isotropic

Oblate

Prolate

DTI

Model

Selection

Anisotropy Maps

90

128

182

146

0.0

0.2

0.4

0.6

D

Ellipsoid Map

Whisker

Plot

Baboon Study Conclusions

• Anisotropy features of fixed baboon brain are remarkably similar to those of live premature infants.
• Models for cortical anisotropy tend to be fairly simple (axisymmetric, prolate, include “constant”).
• Similar information can be obtained from human infants using fewer b or q values (i.e., with shorter scan times than for baboon tissue).
• Studies of tissue from injured baboons (and humans) are under way.

Terrie E. Inder, MD, PhD

Chris Kroenke, PhD

G. Larry Bretthorst, PhD

Robert C. McKinstry, MD, PhD

Amit Mathur, MD

Jeff Miller, MD

I. Alpay Ozcan, DSc

Georgia Schefft, CPNP

Shelly I. Shiran, MD

Joshua S. Shimony, MD, PhD

Avi Z. Snyder, MD, PhD

C. Robert Almli, PhD

NS37357